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G. Dean Price, Murray R. Badger, Susanne von Caemmerer, The Prospect of Using Cyanobacterial Bicarbonate Transporters to Improve Leaf Photosynthesis in C3 Crop Plants, Plant Physiology, Volume 155, Issue 1, January 2011, Pages 20–26, https://doi.org/10.1104/pp.110.164681
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The photosynthetic CO2-fixing enzyme Rubisco arose some 3.5 billion years ago, in an environment when CO2 was high and oxygen (O2) was low. Under these conditions, it was CO2 saturated and presumably performed well (Badger et al., 1998). However, since the advent of oxygenic photosynthesis, the levels of O2 have risen dramatically and CO2 has fallen to very low levels. This has gradually created conditions where CO2 has become limiting for Rubisco and allowed O2 to act as an alternative inhibitory substrate for the enzyme. To cope with these dramatic environmental changes, two major strategies have evolved to help Rubisco maximize its carboxylation rate at ambient levels of limiting CO2. First, the enzyme has evolved better kinetic properties, where the K m(CO2) has decreased and the ability to distinguish against O2 has increased at the expense of catalytic rate (Badger et al., 1998). Alternatively, many photosynthetic organisms, ranging from cyanobacteria to algae to land plants, have developed active CO2-concentrating mechanisms (CCMs) to turbo-charge Rubisco’s CO2 supply at a minor metabolic cost (Badger et al., 1998). Most notably, among plants this has led to the development of C4 photosynthesis (Sage, 2004).
